The objective is to develop a high speed, high resolution laser scanning instrument to measure both the mass and the molecular weight of DNA separated by gel electrophoresis. The instrument detects visible fluorescence from a DNA-specific dye excited by a visible cw laser. Experiments with a slow scanning breadboard instrument have demonstrated 1) a 100X improvement in sensitivity over present photographic methods, 2) the potential for measuring sample fluorescence more accurately by employing improved techniques to control and correct for variation in background fluorescence. The mass of DNA in a band is directly proportional to the summed fluorescence signal. In phase I, the present breadboard will be modified to scan 100X faster with a higher output laser in order to scan a 20cm long gel lane in under 5.0 min. The greater speed and data handling capacity will permit 1) performing the extensive testing required to more fully establish instrumental and analytical performance, and 2) studying further samples in several types of gels. An engineering prototype will be built and extensively tested in Phase II which will use rapid laser beam deflection and a higher power laser to increase the measurement speed by an additional factor of 100X.